"I heard Abu Kabshah Al-Anmari saying: 'The Kimam (caps) of the Companions of the Messenger of Allah (ﷺ) were Buthan (stretched over the head).'"

This Hadith is Munkar, 'Abdullah bin Busr is from Al-Basrah, and he is weak according to the people of Hadith. Yahya bin Sa'eed and others graded him weak. Buthun means expansive.
Jami` at-Tirmidhi Book 24, Hadith 71